Control keyboard for electric or electronic devices

ABSTRACT

A keyboard for electric or electronic devices including a layered composite plate formed with holes through which extend the stems of keys each adapted for controlling one or several electric contacts. The contacts are closed when the corresponding key is in one of its working and rest positions and is open when the key is in its other position. The plate provides for returning the keys by magnetic attraction in cooperation with elements such as soft iron plates or washers rigidly connected to the lower ends of the key stems. The elements are disposed under the plate and are normally maintained in contact with the latter by magnetic attraction thereby determining the rest positions of the keys. The contacts which are controlled by the keys are at least carried by one of the faces of the composite plate and cooperate with closing or opening operating structure associated with the aforementioned keys.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a control keyboard of an electric orelectronic device, of the type comprising a grid or an apertured plateformed with a multiplicity of holes in which are engaged keys eachadapted for controlling one or several electric contacts when they aredepressed.

2. Description of the Prior Art

In the present technology, the keys are generally returned to their restposition by springs. The use of springs leads to many disadvantages:loss of rigidity of the spring, fatigue phenomenon, resonance frequency,bad behaviour to vibrations and accelerations, sensitivity to corrosion,rebound phenomenon when establishing the electric contacts, etc.

It has already been proposed to remove most of said disadvantages byreplacing the return springs with magnetic return means which are inpart carried by the keys themselves, and in part carried or formed bythe aforementioned grid or apertured plate.

This new technique, while presenting many advantages relative to thetraditional art, has nevertheless a disadvantage in that the contacts,which are adapted to be acted upon by the keys when the latter aredepressed, are carried by an independent plate, generally a printedcircuit plate, which is placed under the grid or apertured plate. Thus,a keyboard is composed of three kinds of elements: the keys, the grid orapertured plate, and the printed circuit plate carrying the contact orswitching elements associated with the keys. The mounting of such akeyboard has to be relatively accurate since the printed circuit platecarrying the contact elements has to be disposed under the grid at apredetermined distance from the latter.

A further disadvantage of the known prior art techniques is that theduration of the electrical signal corresponding to the closing of acontact obtained by depressing a key is very short relative to the totaloperation time of the key. However, for some technical reasons, andnotably the electronic processing of said signals, it is often requiredthat the duration of the signal thus established be at least equal to60% of the operation time of the key.

SUMMARY OF THE INVENTION

The object of the present invention is precisely to solve all saidproblems, by simultaneously avoiding the disadvantages of the knownprior art techniques.

Notably, the object of the invention is a monolithic-type keyboard inwhich the grid carrying the keys and the plate carrying the contactelements are united in one single assembly.

Another object of the invention is an improved keyboard of theaforementioned type, in which the duration of a signal obtained bydepressing a key is widely superior to 60% of the total operation timeof the key, and is some cases equal to this total operation time.

Therefore, the invention proposes a control keyboard for electric orelectronic devices, comprising a grid or a composite plate formed withholes through which extend the stems of keys. Each key is adapted tocontrol one or several electric contacts which are closed when thecorresponding key is in one of its working and rest positions and whichare open when the key is its other position, said plate or gridcomprises means for returning the keys by magnetic attraction bycooperating with elements such as soft iron plates or washers rigidlyconnected to the lower ends of the key stems. The elements are disposedunder said plate and are normally maintained in contact with the latterby magnetic attraction, thereby determining the rest positions of thekeys, wherein the contacts which are controlled by the keys are at leastpartly carried by one of the faces of the composite plate and cooperatewith closing or opening operating means associated with the keys.

According to this characteristic of the invention, a monolithic keyboardis obtained in which the grid supporting the keys and the platesupporting the contact elements are united in one single element.

According to a further characteristic of the invention, the contacts arenormally closed when the keys are in their rest position, and are openas soon as the keys leave their rest position.

Thus, a keyboard is obtained wherein the duration of a signal resultingfrom depression of a key is equal to the total operation time of thekey, that is the sum of the depressing time of they key and the timeneeded by it for returning to its rest position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and further objects,characterizing features, details and advantages thereof will appear moreclearly when reading the following explanatory description withreference to the accompanying diagrammatic drawings given by way ofnonlimiting examples only and illustrating various embodiments of theinvention, drawings wherein:

FIG. 1 is a cross-sectional diagrammatic view of a first embodiment of akeyboard according to the invention, with contacts normally closed inthe rest position;

FIG. 2 is a cross-sectional diagrammatic view of a second embodiment ofa keyboard according to the invention, with tight contacts normallyclosed in the rest position;

FIG. 3 is a sectional view at a larger scale of a contact element usedin the keyboard shown in FIG. 2;

FIG. 4 is a partial sectional diagrammatic view of a third embodiment ofa keyboard according to the invention, with tight contacts normally openin the rest position; and

FIG. 5 is a partly sectional diagrammatic view of a fourth embodiment ofa keyboard according to the invention, with tight contacts normallyopen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a partial sectional diagrammatic view of a first embodiment ofa keyboard according to the invention. Said keyboard comprisessubstantially an apertured composite plate 10, keys 11 engaged in theholes of the plate or grid 10, and contact elements 12 mounted on thelower face of the composite plate 10.

Plate 10 can form the front face or a portion of the front face of anelectric or an electronic apparatus, and it is associated with aplurality of keys 11 although one only of said keys has been shown inthe drawing.

The composite plate 10 comprises an upper metallic plate 13, of smallthickness, intended for providing the plate 10 with a sufficientrigidity. On the lower face of the metallic plate 13, made for exampleof iron, soft iron or steel, is glued or bonded a plate 14 made of amagnetic material such as a multipolar magnetic elastomer, the thicknessof which is a function of the magnetic attraction or return forcedesired for application to said keys.

The contact elements 12 are, for example, metallic or metallized contactwafers, made of an electro-conductive material, and which are part of anelectro-conductive network 15 formed on the lower face of a film or thinsheet 16 of insulating material, such as a plastics material. Said filmor said thin sheet 16 is fixed, by any appropriate means, on the lowerface of the magnetic elastomer plate 14.

Advantageously, the film or thin sheet 16 provided on one face with theelectro-conductive network 15 and the contact wafers 12, can be a sheeta flexible plastics material, such as that which is available on themarket under the trade-name of "Mylar," which can be used for making aprinted circuit, either on depositing on one face of said sheet anelectro-conductive ink by a silk-screen process, or by metallizing saidface when processing it in a traditional way.

Of course, the electro-conductive network 15 is coated, with theexception of the wafers 12, with a film or a very thin layer ofinsulating material, for example an insulating varnish.

Each key 11 comprises a head or hood 17, which is mounted, for instanceby a resilient snap-in arrangement, on the upper end of a stem 18 whichextends inside one of the holes 19 formed in the composite plate 10. Atits lower end, the stem 18 is rigidily connected, for example through asnap-in arrangement, ultrasound riveting or any other appropriate means,to a plate or thin washer 20, for example made of soft iron or any othermaterial likely to be magnetically attracted by the magnetic elastomerplate 14.

The contact wafers 12 formed on the thin sheet 16 are arranged in theimmediate vicinity of the holes 19, and corresponding bosses orprotruding studs 21 are formed on the corresponding or registeringsurface of the plate or washer 20.

The keyboard operates in the following manner:

In its rest position, each key 11 is in the position shown in FIG. 1, inwhich the soft iron plate or washer 20, which is rigid with the stem 18,is magnetically attracted by the magnetic elastomer plate 14, being thusapplied on the lower face of the thin sheet 16. In this position, thebosses or studs 21 of the plate or washer 20 bear directly on thecontact wafers 12 and establish an electric connexion therebetween. Thecontacts are therefore normally closed, in the rest positions of thekeys 11.

When a user depresses a key 11 by applying a force which is superior tothe magnetic attraction force exerted by the elastomer plate 14 on thesoft iron washer 20, the key 11 is depressed until the lower edge of itshead 17 comes in abutment against the upper metallic plate 13. Themagnetic attraction force which acts on the plate or washer 20 decreasesin proportion with the driving-in of the key, on the whole length of thekey stroke. This stroke is relatively small, for example of the order ofabout 3 mm, so that the magnetic attraction force exerted by theelastomer plate 14 on the washer 20 is always far superior to the totalweight of the key 11.

As soon as the key 11 leaves its rest position shown in FIG. 1, thestuds or bosses 21 draw away from the contact wafers 12. The resistanceof the circuit between two associated wafers 12 then becomes infiniteand remains at an infinite value as long as the key 11 is not back toits rest position shown in FIG. 1.

It will be understood that, in this way, the duration of the signalobtained by depressing the key 11 is equal to the total operation timeof the key 11 that it requires to be depressed and returned to its restposition. In fact, the signal corresponds to the opening of contacts12-21, which are closed when the key is its rest position.

It is also noted that the quality of a signal obtained by depressing thekey 17 is absolutely independent of the quality of the contact betweenthe wafers 12 and the studs 21, or of the corresponding contactresistance value, since the establishment of said signal by depressingthe key 11 corresponds to a contact resistance of infinite value.

In this way, all the rebound phenomena which could eventually appearpreviously at the moment of the establishment of the signal by closingtwo contacts are also suppressed.

In explanation, it will be stated, by way of a non limitative example,that the upper metallic plate 13 is a plate of soft iron or steel with athickness varying between 0.5 and 1.5 mm that the plate 14 is amultipolar magnetic elastomer plate having a thickness comprised between1 to 2 mm according to the magnetic attraction force which one wishes toobtain, that the thin sheet 16 provided with the electro-conductivenetwork 15 and the contact wafers 12 has a thickness of about 1 tenth ofa mm, the soft iron plate or washer 20 has a thickness of 1 mm, thecontact wafers 12 have a diameter of 5 mm about, the stroke of the key11 is of 3 mm about, the magnetic attraction force applied by the plate14 on the soft iron plate 20 varies between 40 and 150 g depending onwhether the thickness of plate 14 varies between 1 and 2 mm.

In all cases, the magnetic attraction force exerted by the elastomericplate 14 on the washer 20 is far superior to the total weight of the key11 and resists accelerations well over 10 g.

FIG. 2 illustrates an alternative embodiment of the keyboard of theinvention, which differs from the embodiment of FIG. 1 in that thecontacts controlled by the keys 11 are completely tight.

The left-hand side half-view of FIG. 2 shows the key in its restposition, and the right-hand half-view shows the key in its workingposition or at the end of its stroke.

This embodiment of FIG. 2 comprises, as the previous one, a key 11having a head 17 mounted by any appropriate means, for example by aresilient snap-in arrangement, on the upper end of a stem 18 extendingfreely through a hole 31 of a composite grid or apertured plate 30. Thelower end of the key is rigidly connected to a plate or washer 20, forexample of soft iron, placed under the composite plate 30 and comprisingon its upper face studs or bosses 21.

The composite plate 30 comprises an upper metallic plate 13, a plate 14made for example of a multipolar magnetic elastomer, and a thin sheet 16of insulating material the lower face of which is provided with anelectro-conductive network 15 and contact wafers 12, as in theembodiment of FIG. 1.

Contrary to the embodiment of FIG. 1, and as is best seen in FIG. 3,another insulating material thin sheet 32 is fixed on the lower face ofthe thin sheet 16 and on the electro-conductive network 15. This thinsheet 32 may also be made of "Mylar" as the thin sheet 16, and it hassubstantially the same thickness (for example 0.1 mm). The thin sheet 32is cut out, as is shown at 33, at the level of the contact wafers 12 ofthe first thin sheet 16.

On the lower face of said thin sheet 32 is applied another thin sheet34, for example identical to the first thin sheet 16, and the upper faceof which carries also an electro-conductive network 15 and contactwafers 12. The thin sheets 16, 32, 34 are superimposed so that thecontact wafers 12 of two sheets are in register with each other, at thelevel of the cut-outs 33 of the intermediate sheet 32. These threesheets may be fixed to each other in any appropriate way, for example bygluing, ultrasound welding, etc.

Since the thin lower sheet 34 is made of a flexible plastics material,one needs only to apply a very light pressure in the upper direction onsaid sheet, on the level of wafer 12, to deform it and bring the wafer12 of the lower sheet 34 in contact with the wafer 12 of the upper sheet16. When the sheets 16 and 34 are in "Mylar" and have a thickness of 0.1mm about, it has been established that a force of 5 g exerted on a sheet16 or 34 ensures the contact of the two wafers 12.

The embodiment of the keyboard of the invention which is shown in FIG. 2operates in the following manner:

When the key 11 is in its rest position (left-hand side half-view), thestuds or bosses 21 of the washer 20 bear against the lower sheet 34, atthe level of the wafers 12, with a force which is well over the force of5 g which is necessary for bringing in contact the wafers 12 of sheet 34and 16. When the two wafers 12, which are in register, are in contactwith each other, the corresponding contact which is adapted to becontrolled by the key 11 is closed. One needs only to apply on the key11 a force for depressing the key which exceeds the magnetic attractionforce exerted by the elastomer plate 14 on the washer 20. As soon as thekey 11 leaves its rest position, the bosses or studs 21 stop exerting apressure on the lower thin sheet 34, and said sheet, due to itsresiliency, resumes its normal position which is shown in the right-handside half-view of FIG. 2, or in FIG. 3. The wafers 12 in register witheach other are then separated and the contacts are opened. When onestops depressing the key 11, it comes back to its rest position and thecontacts are again closed.

It will be understood that the contacts thus formed by thesuperimposition of the three sheets 16, 32 and 34 are perfectly tightand remain tight for the whole time of use of the keyboard.

The embodiment shown in FIG. 4 corresponds substantially to that of FIG.2 and 3, and differs therefrom only in that the contacts, controlled bythe keys, are normally open in the rest position of the keys.

In the embodiment of FIG. 4 the composite plate 40, or grid, is formedwith two narrow holes 41 for each key, and each key 42 comprises a head43 mounted, in an appropriate manner, on the upper end of two parallelstems 44 extending freely through the holes 41. At their lower end, thetwo stems 44 are rigidly connected to a plate or washer 45 made of softiron or any other similar and appropriate material.

As previously, the composite plate or grid 40 comprises a thin metallicplate 48 on the lower face of which is fixed a plate 47 made of amagnetic material, for example a multipolar magnetic elastomer.

An assembly of thin sheets 16, 32 and 34, exactly similar to that shownin FIG. 2 and 3, is fixed or placed on the upper face of the metallicplate 48, the lower thin sheet 34, being for example, fixed on themetallic plate 48.

In the example shown in FIG. 4, two contact wafers 12 carried by thesheets 16 and 34 respectively, are between the two stems 44 of key 42,and the head 43 of the latter comprises, on its lower face, a stud orfinger 46 protruding downwardly and provided on the vertical of thewafers 12.

When the user depresses the key 42 for displacing it from its restposition shown in FIG. 4 to its working position, the stud or finger 46comes to bear against the upper thin sheet 16 and brings the contactwafer 12 carried by the sheet 16 in contact with the wafer 12 carried bythe lower sheet 34. When the user stops depressing the key 42, themagnetic attraction force exerted by the elastomer plate 47 on the softiron plate or washer 45 brings the key 42 back to its rest position, sothat the stud or finger 46 is drawn away from the upper thin sheet 16,and the latter recovers, by its resiliency, its normal position shown inFIG. 4 wherein the two contact wafers 12 are apart from each other.

It will be understood that in this embodiment, the assembly of the threethin sheets 16, 32 and 34, which are mounted on the upper face of themetallic plate 48, can be protected against outer impacts by a grid, notshown in the drawing, surrounding the heads 43 of keys 42, and formingthe front face of the keyboard.

The alternative embodiment shown in FIG. 5 relates also to a keyboardwith contacts normally open in the rest position of the keys, whereinthe duration of the signal obtained when closing the normally opencontacts is only slightly less than the total duration of the operationof the key.

In this embodiment, each key 50 comprises a head 51 mounted, in anappropriate manner, on the upper end of a stem 52 which extends freelythrough a hole 53 of a composite plate 54, and which is rigidlyconnected, at its lower end, to a plate or washer 55 of soft iron or anyother appropriate and similar material, carrying an upper plate 56 madeof a magnetic material such as a multipolar magnetic elastomer.

The composite plate 54 comprises a metallic plate 57, on the upper faceof which is fixed an assembly of three thin sheets 16, 32 and 34 exactlysimilar to that shown in FIG. 4. On the upper thin sheet 16 of thisassembly is placed or fixed a metallic grid 58 forming the front face ofthe keyboard and which is formed with openings having a dimensioncorresponding substantially to that of the head 51 of key 50.

The embodiment of FIG. 5 differs from that of FIG. 4 in that a hole 59,of relatively small diameter, is formed through the metallic plate 57and the assembly of the three thin sheets 16, 32 and 34, at the level ofthe contact wafers 12 carried by the sheets 16 and 34. A free piston 60comprising an axial stem 61, a head 62 and a foot 63, is mounted in saidhole 59 so that the head 62 bears against the upper thin sheet 16,without exerting a pressure on said sheet, when the key is in its restposition, the foot 63 of the free piston 60 being housed in a recess 64formed to this effect in the metallic plate 57. The length of the stem61 is such that, in this position, the foot 63, which is made of amaterial such as soft iron, is applied by magnetic attraction on theupper face of the magnetic elastomer plate 56.

The operation of this embodiment is the following:

As soon as the user exerts a pressure on the key 50, and when said keyleaves its rest position shown in the drawing, the magnetic elastomerplate 56 which is integral with lower end of stem 52 of the key drawsaway from the plate 57. The magnetic attraction force exterted by saidplate 56 on the foot 63 of the free piston 60 is well in excess of theforce which it is necessary to exert on the upper thin sheet 16 fordeforming it and bringing its wafer 12 in contact with the correspondingwafer 12 carried by the lower thin sheet 34. Thus, as soon as the key 50is depressed and leaves its rest position, the free piston 60 followsthe movement of said key until the wafer 12 of the upper sheet 16 isbrought in contact with the wafer 12 of the lower sheet 34. The freepiston 60 is then blocked and cannot move down any further. It remainsin this position until the key 50 is back to its initial position.

It will be understood that in this embodiment, the duration of thesignal produced by closing the contact is substantially equal or veryslightly lower than the total operation time of the key 50.

One understands that in all the embodiments just described, the keyboardhas a monolithic structure, viz. the composite grid comprising the holesthrough which extend the keys, and the plate or sheets carrying thecontacts which are adapted for being operated by the keys, form a singleunit assembly thereby substantially simplifying the manufacture of saidkeyboards and reducing their cost considerably.

It is noted also that in the embodiments described, the metallic plates13, 40 and 57 have a double function; they serve as reinforcementelement providing the composite plate thus obtained with rigidity, andthey are always situated just above the magnetic elastomer plates 14, 47and 56, which provides the possibility of cancelling the magnetic fieldabove said plates, and to reinforce it quite considerably below saidplates.

Finally, one will remark that the magnetic return forces exerted on thekeys for bringing them back to their rest position and keeping them intheir rest position are always far superior to the weight of the keys,so that the keyboard according to the invention can resist importantaccelerations and vibrations. One should also note that the embodimentsof the keyboard according to the invention, shown in FIGS. 2, 4 and 5,have been subjected to very severe tests. Said tests have allowedestablishing that after 10⁸ manipulations, said keyboards do not exhibitany deterioration or fatigue sign.

The invention is of course not limited to the embodiments described andshown and which were given only by way of examples. In particular, itcomprises all the means forming technical equivalents of the describedmeans, as well as their combinations, provided the latter are carriedout according to its spirit.

What is claimed is:
 1. A keyboard comprising a layered composite platemade from a layer of magnetic material and an electric printed circuitmade on an insulating substrate applied on a lower face of said layer ofmagnetic material, said plate being formed with holes extending throughthe layer of magnetic material and the substrate of the electric printedcircuit, said keyboard further comprising keys having stems extendingthrough said holes, key tops mounted on the stems and soft iron platesmounted on the stems opposite to said key tops and extending under saidcomposite plate, said soft iron plates being magnetically attracted bysaid layer of magnetic material and defining a rest position of the keyswhen applied onto said plate, said soft iron plates further cooperatingwith conductive contact areas of the electric printed circuit forforming switches which are closed when the keys are in their restposition and opened as soon as the keys leave their rest position.
 2. Akeyboard according to claim 1, wherein the said soft iron plates areformed with protrusions cooperating with the said contact areas of theprinted circuit for closing said switches when the keys are in theirrest position.
 3. A keyboard according to claim 1, wherein the contactareas of said printed circuit and the soft iron plates of the keys areelectrically connected to each other when the keys are in their restposition.
 4. A keyboard according to claim 1, wherein said compositeplate further comprises a layer of insulating material fixed on saidprinted circuit and a second printed circuit formed on a face of anelectrically insulating flexible sheet which is fixed by said face onthe said layer of insulating material, said second printed circuithaving contact areas disposed in register to the contact areas of thefirst cited printed circuit, and the layer of insulating material havingcut-outs at the level of said contact areas, so that two contact areasin register can be brought into contact with each other by a said softiron plate of a key when the key is in its rest position.
 5. A keyboardaccording to claim 1, wherein the composite plate comprises an uppermetallic plate covering said layer of magnetic material.
 6. A keyboardcomprising a layered composite plate made from a layer of magneticmaterial and an electric printed circuit formed on an insulatingsubstrate applied on an upper face of the composite plate, saidcomposite plate being formed with holes extending through the saidsubstrate and said layer of magnetic material, said keyboard furthercomprising keys having key stems extending through said holes, key topsmounted on the stems and soft iron plates mounted on the stems oppositesaid key tops and extending under said composite plate, said soft ironplates being magnetically attracted by said layer of magnetic materialand defining, when applied on said composite plate, a rest position ofthe keys, said composite plate further comprising an intermediate sheetof insulating material covering said printed circuit, and an upperinsulating flexible sheet fixed by a face on said intermediate sheet andprovided on said face with an electric printed circuit, both printedcircuits having conductive contact areas in register to one another andthe intermediate sheet having cut-outs at the level of said contactareas, the key tops having protrusions extending downwardly and adaptedfor applying the contact areas of the printed circuits on each otherwhen the keys are brought to a working position.
 7. A keyboard accordingto claim 6, wherein a metallic plate having holes is disposed betweenthe layer of magnetic material and the said insulating substrate.
 8. Akeyboard comprising a layered composite plate including a metallicplate, a first insulating substrate formed with an electric printedcircuit and fixed on an upper face of the metallic plate, an insulatingsheet fixed on said substrate and covering the printed circuit, a secondinsulating substrate fixed by a face on said insulating sheet andprovided on said face with an electric printed circuit, both printedcircuits having contact areas disposed in register to one another andsaid insulating sheet having cut-outs at the level of said contactareas, the said composite plate being formed with holes extendingthrough said metallic plate, said first and second substrates and saidinsulating sheet, said keyboard further comprising keys having key stemsextending through said holes, key tops mounted on the stems and platesof magnetic material mounted on the stems opposite the key tops anddisposed under said composite plate, said plates of magnetic materialbeing magnetically attracted towards said composite plate and defining,when applied on said plate, the rest position of the keys, saidcomposite plate being further provided with holes into which aredisposed free pistons each having a head which bears on the secondinsulating substrate at the level of said contact areas and each havinga foot magnetically attracted by the plates of magnetic material on thekey stems, said contact areas of both printed circuits being applied oneach other by the free piston heads as seen as the keys leave their restposition.
 9. A keyboard according to claim 8, wherein an upper metallicplate having holes covers the said second insulating substrate on saidcomposite plate.